I found the fare you mentioned CVG-BRU for 24-29 November, but not through LAX. Do you happen to have flights/dates for that? Thanks!
I think you're confused about how routings can (and can't) work. LAX is very likely NOT a valid connection city to fly from CVG to BRU (or anywhere else in Europe for that matter). The reason your fares are likely so high is because you are really pricing out:
CVG-LAX (F)
LAX-BRU-LAX (J)
LAX-CVG (F)
Essentially 2 one-way F fares and one r/t J fare.
I could be wrong about LAX not being valid (I've flown MSN-DTW-PDX-AMS-TLS-AMS-PDX-DTW-MSN before as a legal routing...but that was before DL took over).
EDIT: If you're looking for LAX-BRU r/t, that's a different story, but that's not what I'm reading in your post...